1. Field of the Invention
The present invention relates to a wavelength branching filter branching light of a desired wavelength and an optical communication module using the same, particularly, to a wavelength branching filter branching light of a specific wavelength used in the optical communication module and an optical communication module using the same.
2. Description of the Related Art
In an optical communication module that implements a two-way communication, there has been known a two-wavelength mode in which two-way signal lights have different wavelength. Light of 1310 nm wavelength band and light of 1490 nm wavelength band are generally used as signal light. In addition, light of 1650 nm wavelength band is used as monitor light required for a line construction. The construction in which these lights can be respectively separated is required in the optical communication module. The optical communication module which is an optical communication module that implements the two-way communication and has the construction capable of separating light of a plurality of wavelengths is disclosed, for example, in JP-A-10-10354.
In case that the light collecting unit and light emitting unit are disposed along the same axis as a cross section of an optical fiber and orthogonally thereto, respectively, the wavelength branching filter is provided at an intersection position of the optical axes of the light collecting unit and the light emitting unit, thereby branching light. The wavelength branching filter is disposed to be at the angle of 45 degrees to the optical axis, whereby transmitting light of 1310 nm wavelength band, and reflecting lights of 1490 nm and 1650 nm wavelength bands are required.
However, the range of 1490 nm to 1650 nm cannot be simultaneously covered in the mixture of SiO2 and Ta2O5 used as a material of a common multilayer film filter. As the result, a filter that reflects only light of 1650 nm wavelength band is provided in a transmitting light side so that light of 1650 nm wavelength band is not involved in the light collecting unit that collects light of 1310 nm wavelength band. Though, in this case, positioning is required due to the increase in the number of parts, thereby raising the cost thereof.
Further, changing the film material can widen the wavelength range of reflecting light. That is, Nb2O5 or TiO2 with higher refraction index than Ta2O5 may be used. However, the wavelength branching filter is fixed within the optical communication module by UV adhesive, whereby the optical communication module can be manufactured at low cost, but since the UN adhesive cannot be used for this material, another fixing method is required, thereby raising the cost thereof.